In projectors that use phosphors to generate light, for example LARP (Laser Activated Remote Phosphor), phosphor wheels are typically used. In LARP concepts, which use lens systems to collect the converted light and the pump light, a complicated beam path is necessary to recycle the blue radiation components. This is because the total costs of such a light module are mainly due to the provision of the blue laser light.
For this reason, the aim is to use only one light source both for pumping and for providing the blue channel. Blue light, which is not incident on any phosphor, is therefore fed back to the original beam. By using only one light source for the blue channel, considerably more compact light modules can also be produced.
In this context, FIG. 1 shows a method, known from the prior art, for addressing this problem, which is known as “wrap-around.” The light module as a whole is here designated by 10. It comprises a laser apparatus 12 which is adapted to emit linearly polarized radiation in the blue wavelength range. Said radiation passes through a first beam splitter 14 which is adapted to transmit radiation in a wavelength range λ<465 nm (HT=highly transmissive) and to reflect radiation in a wavelength range λ>465 nm (HR=highly reflective). The radiation emitted by the laser apparatus 12 thus passes through the mirror 14 and impinges on a focusing apparatus 16, which is arranged between a beam splitter 14 and the luminous wheel 18.
In the light module 10, the luminous wheel 18 is shown in a side view, while in FIG. 1 it is shown at the bottom right in plan view. The luminous wheel 18 is rotatably mounted on a spindle 20 and in the present case has a region 22a, which is coated with a phosphor which converts the radiation in the blue wavelength range impinging on it into the red wavelength range. A region 22b comprises a phosphor which is adapted to convert the radiation in the blue wavelength range impinging on it into the green wavelength range, while a region 22c is coated with a phosphor that is adapted to convert the radiation in the blue wavelength range impinging on it into the yellow wavelength range. The region 24 has a slit, i.e. when this region in the light module of FIG. 1 is arranged at the top, the excitation radiation can pass through the luminous wheel 18 without being obstructed. The radiation emitted by the regions 22a, 22b, 22c passes through the focusing apparatus 16 and impinges on the mirror 14. Owing to the changed wavelength, this radiation is then reflected at the mirror 14.
However, the radiation passing through the slitted region 24 of the luminous wheel 18 impinges on a collimating apparatus 26 and subsequently in series on in the present case three deflection mirrors 28a, 28b, 28c. The last deflection mirror 28c directs the radiation onto the beam splitter 14, through which the radiation passes such that the blue radiation components are superposed onto the radiation components converted by the phosphors and are then guided to the entry aperture 30 of a projection engine 13.
The problem with the light module 10 illustrated in FIG. 1 is the space needed for this purpose. In particular in portable applications it is desirable if the light module used requires as little installation space as possible. Another disadvantage of the light module illustrated in FIG. 1 is the large amount of outlay for mounting the various optical components, which also results in undesirably high production costs.